With ordinary computers, it is often the case that numerical or character data of a discrete nature almost irrelevant to one another are processed together. And, when recording or reproducing discrete signals representing such discrete data information, no error with regard to any signal is, as a rule, permissible. If, therefore, there should be any defect or missing part about the data contained when such discrete signals recorded in an optical disk or the like are to be reproduced, it is essential to restore the original data perfectly.
Hence, recording discrete signals such as mentioned above has to be made by a highly reliable recording method capable of restoring original data by the use of a powerful error-correcting means.
However, with regard to continuous signals representing continuous analog information such as music or video-information, there is a strong interrelation between adjacent pieces of data. Hence if there should be some defect or missing part in a given data, correction by interpolation is feasible to some extent by the aid of an error-correcting means with its presuming capability. Thus, there is little worry about any fatal damage.
Moreover, this error-correcting means, compared with the aforementioned counterpart, has the advantages of being less in the required number of redundant bits and simplified in circuit composition. Further, it is capable of largely compressing data, this resulting in a substantially longer time of recording.
With such continuous signals, a significantly larger amount of information is recordable on the medium as compared with discrete signals.
Conventional optical disk recording and reproducing devices seldom record discrete signals and continuous signals together. By recording mixed signals on an optical disk, the treatment required for recording the discrete signals has to be applied to all signals; thus resulting in an increased loss in recording continuous signals and in a decreased storage capacity.
Some known a types of optical disks are capable of recording various signals such as a CD-ROM [Compact Disk-ROM]. With CD-I [Compact Disk-Interactive Media], it is possible to record discrete signals consisting of application programs and continuous signals representing video- and audio-information in the CD-I region along the inner periphery of the disk. In the outer peripheral region of this CD-I it is also possible to record digital audio signals of a CD-type.
These known types of CD-ROM were invariably intended for recording signals in the form of pits fixed on the disk and hence only suitable for reproduction or play-back.